Composite materials can include a filler dispersed in a polymer matrix. The filler, especially if it is an inorganic one such as clay, can contribute to the mechanical properties of the composite, such as stiffness. In traditional composites, certain other properties, such as impact resistance, may suffer as a result of incorporation of the filler. More recently, a new class of composite materials, known as nanocomposites, has received considerable attention. Unlike conventional composites, which tend to lose impact strength with increasing filler levels, nanocomposites generally retain high levels of impact strength while enhancing the thermal, physical, and mechanical properties of the composite relative to that of the parent polymer alone. In nanocomposites, these material property enhancements are frequently observed at much lower inorganic loading levels than are normally used for conventional fillers. Industrially useful polymers whose properties may be enhanced through nanocomposite formation include poly(meth)acrylates, polystyrenes, polyolefins, nylons, polyesters, polycarbonates, (block) copolymers containing these units, and fluoropolymers such as polytetrafluoroethylene, polyvinylidene fluoride, etc.
Commonly used fillers for making nanocomposites include clays such as montmorillonite, bentonite, laponite, and other mica-type aluminosilicates. The desirable properties of clay-containing nanocomposites may be due, at least partly, to intimate interactions between the host polymer and the interstitial galleries of the clay, especially when the latter has been rendered more organophilic via cation exchange reactions with organic cations.
Nanocomposites can be prepared either by in situ polymerization (solution, emulsion, batch, bulk, etc.), melt intercalation, solution casting, or other techniques. During these processes, wetting of the surface of the clay with the polymer may be enhanced by the presence of the organic cationic modifiers, which are intercalated into the clay galleries. This cation intercalation facilitates parent polymer intercalation into the interstitial spaces between the clay layers, thus aiding clay platelet exfoliation. The optimal cation for facilitating this process depends upon a number of factors, including the type of polymer(s) to be incorporated in the composite, stability during material processing, and desired nanocomposite material properties, and therefore it is desirable to be able to provide intercalating cations that are functionalized with any of a variety of organic groups, typically some fraction of cation modifiers, whether a small (monomeric) or large (oligo- or polymeric) cationic molecule that are of a similar composition to that of the polymers that will be mixed with the clay to form the nanocomposite. However, this cation modifier compositional characteristic does not preclude other potential characteristics one skilled in the art may use such as polar and non polar, van der Waal's, or covalent interactions to impart and enhance desirable end material properties.